The present invention relates to auto electronic flash units.
In the past with conventional auto-flash units there is a critical distance point between the flash unit (i.e. camera) and the object being photographed at which auto control is possible but beyond this distance (i.e. the critical point) proper exposure could not be obtained because of insufficient exposure. Therefore it is important and necessary to inform the camera operator whether or not the proper exposure for the film is possible. Conventional auto-flash units operate by a photosensing device which receives reflected light from the subject, detects an electric signal which is produced when the reflected light reaches a pre-determined level and then interrupts the illumination of the flash unit. Accordingly with these conventional auto-flash units the camera operator is only informed when the interruption of the illumination occurs. However, there is some distance beyond the maximum distance of the auto control at which proper exposure is possible due to the latitude of the film and error inherent in guide numbers. Because of these features the range of conventional auto-flash units for photography is narrow.